Although drug use has declined substantially over the past two decades, it remains a serious problem in the U.S., as almost twelve percent of the population still used illicit drugs during the past year. Moreover, prevalence rates for most groups have remained fairly stable over the past few years, and appear to be rising for young adults. Minority groups, tend to be over-represented among those who suffer from the adverse health and social consequences associated with drug use, although they report similar or lower levels of drug use, and differences in socio-economic status does not fully account for the differences in the adverse health and social outcomes. Much prior research has focused on the short-term effects of adolescent drug abuse rather than on the possible long-term effects of drug abuse, and has not devoted enough attention to the importance of childhood living arrangements and sibling behavior. There are important racial and ethnic differences in patterns of drug use and these family factors, and these differences may help account for observed racial and ethnic differences in the adverse health and social associated with drug abuse. The proposed study will use the National Longitudinal Survey of Youth, a large nationally representative longitudinal data set that has followed respondents for 18 years, to examine the timing pattern of the effects of drug use to determine whether detrimental effects of drug abuse only appear when there is persistent or long-term drug use. The proposed study will also examine whether the types of drugs used and their intensity of use matter. The NLSY also contains detailed information on childhood living arrangements and on older siblings' adverse health and social outcomes, including drug use, and the proposed research will employ these data to examine how these family factors are associated with drug use and adverse health and social outcomes. Throughout the proposed analysis, we will examine the extent to which family factors account for observed racial and ethnic differences in drug use, how differences in these factors and drug use account for differences in adverse outcomes, and estimate how the effects of each of these factors vary by race and ethnicity. We will also test and control for possible unobserved factors and reciprocal effects that may bias empirical estimates.